1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method generating an edge image of characters from a color document, gray scale document and the like.
2. Description of the Related Art
In character recognition technology for a color document, gray scale document and the like, a technique called edge detection is used in order to obtain an image in which outlines of characters in the document are separated from the background. This edge detection is a method of detecting a change in value (difference value) of density, color and the like between adjacent pixels (refer to Japanese Patent Laid-open Application No. 2001-175808 (paragraph 0010 and soon), for example). Thereby, the edge image corresponding to the outlines of the characters can be obtained from, for example, the image in which the density of the characters is higher than the density of the background, and the like.
However, when the edge image is generated by using absolute values of the difference values of the density, color and the like between the adjacent pixels as they are, there are tendencies that the so-called inside void is caused with the part along the outline of the character being thick and inside thereof being light, and line width of the character broadens. This causes the problems that the characters contact each other and the image with high readability of characters is hardly obtained.